Our invention relates to an apparatus for data transfer with interchangeable disklike record media such as flexible magnetic disks which may be packaged in cassette or cartridge form. More specifically, our invention dealas with such an apparatus for use with a flexible magnetic disk or or the like having a first opening defined centrally therein for receiving a drive spindle on a turntable included in the apparatus, and a second opening defined eccentrically therein for receiving a retractable drive pin arranged eccentrically on the turntable.
The above defined type of flexible magnetic disk and an associated data transfer apparatus or disk drive have both been suggested by Sony Corporation., of Tokyo, Japan, as disclosed in Japanese Laid Open Patent Application 57-36473, laid open to public inspection on Feb. 27, 1982, and in corresponding U.S. Pat. No. 4,445,155 issued Apr. 24, 1984. This known flexible magnetic disk has a diameter of 3.5 inches (86 millimeters) and is rotatably housed in generally flat, boxlike envelope of relatively rigid plastics material to make up a disk cassette. Aside from its size, the magnetic disk differs from more conventional ones in having a metal made center hub to be placed concentrically on a motor driven turntable included in the associated data transfer apparatus. The hub has a central hole for receiving the spindle projecting from the turntable, and an eccentric slot for receiving a retractable, spring energized drive pin mounted eccentrically on the turntable.
A problem with this type of magnetic disk and data transfer apparatus for use therewith is the engagement of the spindle and drive pin in the respective opening in the disk hub. Of course, the spindle finds ready engangement in the center hole in the disk hub as the magnetic disk is loaded concentrically on the turntable. Except in very rare cases, however, the drive pin is out of register with the eccentric slot in the hub of the magnetic disk when the latter is placed on the turntable, and so does not become engaged therein unless the turntable is revolved relative to the disk.
Consequently, when the disk drive motor is subsequently set into rotation, as in response to a "motor on" signal from host equipment controlling the data transfer apparatus, the magnetic disk starts rotation with some delay, only after the engagement of the drive pin in the eccentric slot in the disk hub. Such delay that has been unavoidable in the conventional data transfer apparatus of this class has correspondingly retarded the commencement of data transfer between the magnetic disk and the transducer heads in response to the "motor on" signal. Furthermore, even if the magnetic disk is once properly engaged with both the spindle and the drive pin on the turntable, it has been possible that the magnetic disk be displaced out of proper engagement therewith when the power switch is opened, or by external shocks during the nonsupply of power. In that case a delay in the start of data transfer has occurred again when, with the power switch reclosed subsequently, the disk drive motor is set into rotation in response to the "motor on" signal.